Crafting effective marketing email content is just one of the fundamentals that can make an effective email outreach successful. In the realms of email marketing the technical aspects are just as crucial as the marketing ploy; our research team devoted their time to understanding the best and most helpful technical factors that can help every email user and marketer with the ability to achieve the best email deliverability and reputation.
For this research, our team examined how different warm-up strategies affect the deliverability of emails from newly created domains.
We’ve tested various flows, each focusing on different approaches that includes:
- Gradual and moderate volume increases
- Passive engagement
- Content diversification
- Mailbox redirect assessment
- Delayed sending
- Platform-specific warm-ups,
- Platform diversity testing
Our objective is to determine the best practice for optimizing domain reputation and ensure high deliverability rates.
A Deeper Look Into Our Research’s Objectives
One of the many reasons why your emails are probably going to spam or junk is because you have a new email or domain.
Many Internet Service Providers (ISPs) may have an issue with new or inactive email addresses when it comes to sending bulk, or large quantities of emails.
ISPs do not have any established data for new domains and inactive mailboxes, so when these new or inactive emails send a large number of messages there is a large chance that it may direct their message to spam. Email warmup is, therefore, crucial in establishing a trustworthy sender reputation before large-scale outreach.
What We Did and How We Did It
Our research team conducted a comprehensive series of tests involving different email platforms and diverse domain configurations.
The majority of focus groups were using Custom SMTP mailboxes as senders and GSuite and MS365 Mailboxes as receivers. Some warm-up strategies we’ve applied include.
Volume Adjustments
To help us assess the impact on sender reputation and inbox placement we’ve included gradual and moderate scaling of daily email volumes ranging from 15 to 200 emails per day.
Content Variation
We’ve also considered that content complexity may have a significant contribution to email deliverability. To do this, we’ve evaluated different templates such as plain text, light HTML, and rich HTML.
Platform Diversity Testing
Cross-testing multiple platforms from Gsuite to Gmail and Microsoft 365 to Outlook to determine and observe platform-specific behaviors.
Redirect and Inactivity Assessments
Understanding how mailbox redirects and delayed sending periods are also crucial in this pursuit of understanding how it affects deliverability performance.
Monitoring Tools and Utilization of Warmy Placement Checker
Warmy’s inbox placement checkers, provided us with the necessary data to track the deliverability performance across different test flows and platforms. With the help of other tools such as MX Toolbox (Blacklist Checker), MS SNDS (Microsoft Smart Network Data Services).
Technical Details that helps Develop Our Research
Senders: Custom SMTP, Gsuite, Microsoft 365
Receivers: Gsuite and Microsoft 365 mailboxes
Total Domains Used: 42
Total Mailboxes: 114 (90 Custom SMTP, 12 Gsuite, 12 MS 365)
Warm-Up Duration: 4–8 weeks (depending on the flow)
Warm-Up Volumes:
- Gradual Increase: 15 to 30 emails/day
- Moderate Increase: 20 to 200 emails/day
- Passive Engagement: No initial sending, followed by 10 to 25 emails/day
- Platform-Specific: 15 to 30 emails/day (Gsuite and MS365)
- Content Diversification: 15 to 30 emails/day (Plain Text, Light HTML, Rich HTML)
Testing Tools: Warmy (Placement Checker),
Key Performance Indicators: Deliverability rates, spam folder incidents, placement performance post-SEM FRESH listing removal
Master Documentation: Centralized master spreadsheet with all domains and mailboxes, including separate tabs per flow
Special Configurations: Gsuite and MS365 domains each configured under unique workspaces without repetition across flows.
Major Breakthrough About Improving Email Deliverability
Gradual Volume Increase
Deliverability improved gradually, reaching 90+% after the 2nd week
The chart illustrates how gradual email volume can provide a positive impact for email deliverability.
It shows an initial low inbox placement rate, but steadily improves as the domain reputation builds.
A key turning point is visible when the domain clears from spam lists such as SEM FRESH (varies from 5 to 7 days from domain to domain), after which inbox placement reaches optimal levels.
This confirms that slow and controlled warm-up strategies help establish a strong sender reputation.
Control Group (No Emails Sent)
Minimal changes in deliverability, highlighting the importance of active engagement.
This chart highlights how non-email activity impacts deliverability. Unlike active warm-up strategies, reputation improves slightly faster than in Gradual Volume Increase focus group (chart above).
This suggests that leaving a domain untouched for a few days after purchase may contribute to better initial deliverability.
However, despite showing results the overall improvements pales in comparison against the Gradual Volume increase group, reinforcing that while maintaining passive aging might offer a slight advantage, active engagement is still necessary to build long-term domain reputation effectively.
As soon as the first emails start to go out from the addresses tested in this focus group — we’ve witnessed a deliverability drop of 60% in some cases.
One-Month Delay
Despite the assumptions that inactivity for a month would improve reputation, the result presented no significant preliminary advantage over domains that started sending immediately.
Deliverability only improves after active sending begins, suggesting that delaying a warm-up does not provide a shortcut to higher inbox placement.
Instead, early engagement paired with a structured warm-up achieves better results.
What Are The Results?
Consistent Deliverability Across Strategies
Gradual volume increases of emails steadily improved inbox placement rates, demonstrating that a slow and controlled approach is effective in building sender reputation.
Moderate increases achieved faster results but came with slight risks, such as temporary dips in deliverability during sudden volume spikes, which also further proves that email campaign volumes should be as gradual as possible.
Platform-Specific Performance
Gsuite achieved optimal deliverability more quickly, consistently maintaining higher inbox placement rates. Microsoft 365 showed a need for tailored warm-up adjustments, with certain configurations requiring extended warm-up periods.
Minimal Content Sensitivity
Deliverability remained stable across different email content formats.
While rich HTML templates initially showed minor fluctuations, overall performance across plain text, light HTML, and rich HTML content types remained consistent, suggesting content complexity plays a minimal role when warm-up processes are properly managed.
Enhanced Performance Through Platform Alignment
Business-to-consumer communications showed higher success rates when sender and recipient platforms were aligned.
Additionally, Gsuite-to-Gmail configurations demonstrated superior initial deliverability rates compared to Microsoft 365-to-Outlook, suggesting a positive contribution from ecosystem alignment, as well as Gsuite and Gmail mailboxes’ more lenient policies regarding email sending, contributing to this outcome.
Spam List Behavior and Clearance Timelines
The clearance from common spam lists, or blacklists, such as SEM FRESH, consistently resulted in immediate improvements in deliverability.
Our team observed that domains usually stay in SEM FRESH spam list 5-7 days after its creation. Domains tested across various flows showed that spam list clearance is a critical milestone, regardless of the warm-up strategy employed
General Conclusion and Recommendations for Future Warmup Processes
Spam List Clearance is Important
The most critical factor influencing deliverability was the domain’s presence on the SEM FRESH spam list. In almost all flows, deliverability rates jumped to 95-100% immediately after the domain left the SEM FRESH list, a real-time blocklist that updates frequently and flags IP addresses involved in suspicious or spam-like activity.
Tailored Warm-Up Strategies
Gsuite-to-Gmail configurations showed superior deliverability compared to MS365-to-Outlook configurations. Differentiated strategies for Gsuite and MS365 are essential for optimal deliverability. MS365 requires more attention to achieve high deliverability.
By using platform-specific tools like Warmy’s free email deliverability test, MS SNDS (Microsoft Smart Network Data Services) for MS365 domains, and Google Postmaster for Gsuite/Gmail domains both platforms achieved 100% deliverability with tailored warm-up processes..
Conduct Initial Template Testing
Content complexity did not significantly affect deliverability. However, Rich HTML templates initially showed lower deliverability in Gradual Volume Increase, suggesting initial content testing is still prudent.
Although content complexity had little effect, testing templates for deliverability remains a best practice. Simpler email bodies tend to perform better across all platforms, but testing exact impacts between ESPs is advised.
Volume Scaling
Gradual volume increase built reputation steadily, while moderate volume warm-up accelerated reputation building but showed dips during volume spikes.
Both gradual and moderate volume increases are effective, with moderate increases posing a higher initial risk.
Ecosystem or Platform Alignment
Platform diversity testing demonstrated that both Gsuite and MS365 could achieve consistent 100% deliverability with tailored warm-up processes.
Aligning sender and recipient platforms enhances deliverability outcomes. MS365 is more trusting of Outlook, and Gsuite performs better with Gmail. For B2C communications, matching platforms between sender and recipient is advisable.
So How Long to Warm Up a Newly Created Domain?
According to our findings, a structured warm-up can take up to 2 to 4 weeks, depending on the approach and platform used. Gradual increase in email volume provides steady improvements, while providing significant gains occurring after the first two weeks.
Meanwhile, passive domain aging — or no sending — for a few days may offer a slight initial boost, however active warm up will remain essential for long-term reputation building.
Clearing spam lists, or blacklists, like SEM FRESH is also important. Once it is removed, deliverability can jump up to 95% to 100%.
So if you have a new email, and you are planning to use it for your cold email outreach, you should dedicate at least 3-4 weeks for a structured warm-up before fully scaling your campaigns.
Our studies enable us to determine that adopting a gradual warm-up strategy, aligning platforms, and prioritizing spam list clearance ensures email reliability and provides guarantee that their emails reach their intended audience, strengthening overall email performance.
Warmy’s Contribution for Your Email Reputation
This study underlines the importance of how a well planned and structured warm-up process, combining content flexibility, tailored platform strategies and platform alignment offers the most effective approach.
Regardless of the warm-up strategy, removing domains from spam lists led to immediate improvements in deliverability, emphasizing the need to expedite this process. Additionally, content complexity has minimal impact when warm-up procedures are properly managed, allowing businesses greater flexibility in crafting email content.
Warmy’s free email deliverability test is instrumental in understanding the contribution of each flow and method, by providing a detailed deliverability score. For email users, this is critical for evaluating email reputation.
It can quickly check if your emails are landing on its intended recipient and shows the percentage of emails that ends in spam, promotions, inbox, and unreceived across major email providers.
Furthermore, it is capable of revealing if your domain or IP is listed anywhere on any blacklists. However, here at Warmy, we also pride ourselves in being an all-in-one email deliverability platform that can help you achieve your email marketing goals.
- We can automate the actual process of “warming up” new email domains by imitating natural email activity.
- With Warmy.io’s Email Seed List providing a more efficient way to accelerate email warming and improve sender reputation, it provides a next-level approach by imitating real human behavior and sending strong positive signals to email providers.
- Furthermore, Warmy’s new Domain Health hub allows users to monitor deliverability at the domain level.
Check out our last report article: Maximizing Email Deliverability: Grouped Vs Randomized Sending
